The present disclosure relates generally to magneto rheological fluid (MR) devices, and particularly to a MR clutch having high torque transfer capability.
MR fluids are a suspension of magnetizable particles, typically pure iron in the micron particle size range, suspended in a carrier fluid, typically a hydrocarbon oil. When this fluid is exposed to a magnetic field, the yield stress of the MR fluid increases by several orders of magnitude. This yield stress change is produced by the formation of columns of magnetizable particles across the gap containing the fluid in the direction of the applied magnetic field. This increase in yield stress can be used to control the fluid coupling between two rotating members, such as in a clutch, or change the flow rate of the fluid through a pipe, channel, or orifice. This change in yield stress is rapid, taking place in milliseconds, and reversible. Since the magnetic field can be rapidly controlled by the application of a current to a field coil, the yield stress of the fluid, and thus the clutch torque, for example, can be changed just as rapidly.
In an effort to utilize this phenomenon, MR clutches have been developed. However, MR clutches suffer from a number of drawbacks, one of which is the relatively low torque density compared to other technologies such as hydraulically actuated clutches, and another is the amount of electrical power consumption required to effect a desired torque transfer via the MR fluid for a given device size. This results in large clutches and/or high power consumption. Accordingly, there is a need in the art to provide MR devices, such as a MR clutch, having improved torque transfer capability and efficiency.